Evolution and biology of colletotrichum truncatum in Canada

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Sexual compatibility and reproduction in fungi is varied and ranges from organisms that are self-fertile and do not require a partner for sexual reproduction, to other groups that have highly complicated mating systems. Understanding the mating system of fungi is fundamental to understanding these organisms as biological species, their potential to exchange genetic information, their ecology and evolution. Among the ascomycetes, a group of fungi including many important plant pathogens, species tend to be either self-fertile, or require a mate with a different mating type (MAT) gene. These genes typically have two forms: MAT1-1 and MAT1-2. Populations of ascomycetous fungi with this mating system consist of two groups, one with the MAT1-1 and the other with the MAT1-2, and it requires one of each for sexual reproduction. However, not all ascomycetes have this system, including Colletotrichum truncatum, causal agent of leaf blight or anthracnose that can cause yield losses of up to 70% on lentil, a major crop on the Canadian prairies . Mating experiments have shown that this fungus also requires genetically different partners for mating, but all isolates had the MAT1-2, and none had the MAT1-1 gene. The first objective of this project is to unravel the genetic control of mating in this fungus by conducting mating experiments and by analyzing whether the MAT1-2 gene is involved in sexual reproduction. Two races have been reported in this fungus, and the more aggressive race appears to be associated specifically with one of the two sexual compatibility groups. Hence another objective is to find out if there is indeed a connection between mating and virulence. Inducing this fungus to sexually reproduce in the laboratory is simple, but has not been seen in lentil fields. Compatible isolates occur on the same plant, so there is a high likelihood for mating to happen in the field. However, the population of this fungus is genetically very similar, and this raises the question of the origin of this fungus. Introduction on infected lentil seed from abroad is one option, living on one or several of the many native species belonging to the legume family like lentil, the other. So the third objective is to elucidate its origin in Canada.